1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of handling anchor-based mobility management and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of a universal mobile telecommunications system (UMTS), for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
An LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmission/reception, UL multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
Please refer to FIG. 1, which shows a schematic diagram of a conventional communication system 10. As shown in FIG. 1, a UE may experience more frequent handovers in small cell deployments compared to homogeneous network deployments. Due to mobility management, frequent handovers would result in large overhead in control signalling (i.e., the messages of Path Switch Request and Path Switch Request Ack) to the core network. For example, if the UE quickly moves around and passes through multiple small cells, the UE may experience more handovers in the small cell environment. To solve this issue, the communication system may employ anchor-based mobility management to reduce the control signalling sent to the core network. However, the anchor base station may suffer heavy load or the anchor base station may be crashed unexpectedly in certain situations. In such situations, the system performance is significantly decreased due to the anchor-based mobility management.
Thus, how to handle the anchor-based mobility management to overcome the tradeoff problem between reducing core-network control signaling, increasing load of anchor eNB, and increasing additional inter-eNB signaling is an important topic to be addressed.